The state of the art of traffic sign recognition by means of surroundings sensors in a car, in particular of the recognition of speed limits by means of a camera system, consists in coupling the driver assistance system with a navigation system in order to obtain additional information from the digital road map stored therein, wherein said navigation system is available in the vehicle. Said additional information is necessary for informing the driver of the current speed limit as precisely as possible. Depending on the specific application of the driver assistance system, camera systems, radar systems, lidar systems or ultrasonic systems are used as surroundings sensors.
For example, the state-of-the-art industrialized cameras in vehicles are still unable to make use of place name signs for recognizing that the vehicle is entering a built-up area and therefore obtain speed limit information from the digital road map and from the current place from the GPS navigation system.
Coupling the surroundings sensor with a navigation system results in considerable extra costs of the driver assistance system.